Merge pull request #2699 from eeckstein/conformance-linkage

IRGen: Don't emit externally available witness tables.

Author: eeckstein

lib/IRGen/GenProto.cpp

@@ -1586,12 +1586,11 @@ void IRGenModule::emitSILWitnessTable(SILWitnessTable *wt) {
   if (wt->isDeclaration())
     return;
 
-  bool mustEmitDefinition = !isAvailableExternally(wt->getLinkage());
-
-  // Don't emit a witness table that is available externally if we are emitting
-  // code for the JIT. We do not do any optimization for the JIT and it has
-  // problems with external symbols that get merged with non-external symbols.
-  if (IRGen.Opts.UseJIT && !mustEmitDefinition)
+  // Don't emit a witness table that is available externally.
+  // It can end up in having duplicate sumbols for generated associated type
+  // metadata access functions.
+  // Also, it is not a big benefit for LLVM to emit such witness tables.
+  if (isAvailableExternally(wt->getLinkage()))
     return;
 
   // Build the witnesses.
@@ -1614,13 +1613,7 @@ void IRGenModule::emitSILWitnessTable(SILWitnessTable *wt) {
   global->setAlignment(getWitnessTableAlignment().getValue());
 
   // FIXME: resilience; this should use the conformance's publishing scope.
-  if (mustEmitDefinition) {
-    wtableBuilder.buildAccessFunction(global);
-  }
-
-  // Build the conformance record, if it lives in this TU.
-  if (!mustEmitDefinition)
-    return;
+  wtableBuilder.buildAccessFunction(global);
 
   // Behavior conformances can't be reflected.
   if (wt->getConformance()->isBehaviorConformance())

test/IRGen/existential_metatypes.sil

@@ -19,6 +19,9 @@ extension Float : Kindable {
   public var kind: Int { get }
 }
 
+// CHECK: @_TWPSi21existential_metatypes8KindableS_ = external global i8*, align 8
+// CHECK: @_TWPSf21existential_metatypes8KindableS_ = external global i8*, align 8
+
 sil @int_kind_getter : $@convention(method) (Int) -> Int {
 bb0(%0 : $Int):
   %2 = integer_literal $Builtin.Int64, 0
@@ -62,15 +65,15 @@ bb0:
   %1 = metatype $@thin Int.Type
   %2 = metatype $@thick Int.Type
   %3 = init_existential_metatype %2 : $@thick Int.Type, $@thick Kindable.Type
-  // CHECK-NEXT: store i8** getelementptr inbounds ([1 x i8*], [1 x i8*]* @_TWPSi21existential_metatypes8KindableS_, i32 0, i32 0), i8*** [[T0]], align 8
+  // CHECK-NEXT: store i8** @_TWPSi21existential_metatypes8KindableS_, i8*** [[T0]], align 8
   store %3 to %0 : $*@thick Kindable.Type
   // CHECK-NEXT: [[T0:%.*]] = getelementptr inbounds { %swift.type*, i8** }, { %swift.type*, i8** }* [[V]], i32 0, i32 0
   // CHECK-NEXT: store %swift.type* @_TMSf, %swift.type** [[T0]], align 8
   // CHECK-NEXT: [[T0:%.*]] = getelementptr inbounds { %swift.type*, i8** }, { %swift.type*, i8** }* [[V]], i32 0, i32 1
   %5 = metatype $@thin Float.Type
   %6 = metatype $@thick Float.Type
   %7 = init_existential_metatype %6 : $@thick Float.Type, $@thick Kindable.Type
-  // CHECK-NEXT: store i8** getelementptr inbounds ([1 x i8*], [1 x i8*]* @_TWPSf21existential_metatypes8KindableS_, i32 0, i32 0), i8*** [[T0]], align 8
+  // CHECK-NEXT: store i8** @_TWPSf21existential_metatypes8KindableS_, i8*** [[T0]], align 8
   store %7 to %0 : $*@thick Kindable.Type
   %9 = tuple ()
   // CHECK-NEXT: bitcast

test/IRGen/sil_witness_tables.swift

@@ -36,6 +36,7 @@ struct Conformer: Q, QQ {
   func qMethod() {}
 }
 
+// CHECK: [[EXTERNAL_CONFORMER_EXTERNAL_P_WITNESS_TABLE:@_TWPV39sil_witness_tables_external_conformance17ExternalConformerS_9ExternalPS_]] = external global i8*, align 8
 // CHECK: [[CONFORMER_Q_WITNESS_TABLE:@_TWPV18sil_witness_tables9ConformerS_1QS_]] = hidden constant [2 x i8*] [
 // CHECK:   i8* bitcast ([4 x i8*]* [[CONFORMER_P_WITNESS_TABLE:@_TWPV18sil_witness_tables9ConformerS_1PS_]] to i8*),
 // CHECK:   i8* bitcast (void (%V18sil_witness_tables9Conformer*, %swift.type*, i8**)* @_TTWV18sil_witness_tables9ConformerS_1QS_FS1_7qMethod{{.*}} to i8*)
@@ -47,7 +48,6 @@ struct Conformer: Q, QQ {
 // CHECK:   i8* bitcast (void (%V18sil_witness_tables9Conformer*, %swift.type*, i8**)* @_TTWV18sil_witness_tables9ConformerS_1PS_FS1_14instanceMethod{{.*}} to i8*)
 // CHECK: ]
 // CHECK: [[CONFORMER2_P_WITNESS_TABLE:@_TWPV18sil_witness_tables10Conformer2S_1PS_]] = hidden constant [4 x i8*]
-// CHECK: [[EXTERNAL_CONFORMER_EXTERNAL_P_WITNESS_TABLE:@_TWPV39sil_witness_tables_external_conformance17ExternalConformerS_9ExternalPS_]] = available_externally constant [0 x i8*]
 
 struct Conformer2: Q {
   typealias Assoc = AssocConformer
@@ -66,7 +66,7 @@ func erasure(c c: Conformer) -> QQ {
 
 // CHECK-LABEL: define hidden void @_TF18sil_witness_tables15externalErasureFT1cV39sil_witness_tables_external_conformance17ExternalConformer_PS0_9ExternalP_(%P39sil_witness_tables_external_conformance9ExternalP_* noalias nocapture sret)
 // CHECK:         [[WITNESS_TABLE_ADDR:%.*]] = getelementptr inbounds %P39sil_witness_tables_external_conformance9ExternalP_, %P39sil_witness_tables_external_conformance9ExternalP_* %0, i32 0, i32 2
-// CHECK-NEXT:    store i8** getelementptr inbounds ([0 x i8*], [0 x i8*]* [[EXTERNAL_CONFORMER_EXTERNAL_P_WITNESS_TABLE]], i32 0, i32 0), i8*** %2, align 8
+// CHECK-NEXT:    store i8** [[EXTERNAL_CONFORMER_EXTERNAL_P_WITNESS_TABLE]], i8*** %2, align 8
 func externalErasure(c c: ExternalConformer) -> ExternalP {
   return c
 }